Noise filter



Original Filed Sept. 18, 1942 i m. l

BY y( f Patented May 9, 1950 NOISE FILTER William M. Robinson, Fairhaven, Mass., assignor to Cornell-Dubilier Electric Corporation, South Plainfield, N. J., a corporation of Delaware original appiieancn september is, 1942, serial No. 458,892.A Divided and this application August 2, 1945, serie-i No. 608,442 Y 6 Claims. 1

This application is a division of application Serial No. 458,892, led September 18, 1942, and entitled Electrical lter, now Patent No. 2,383,-

The present invention relates to antiinterference or noise filters, more particularly to tuned lters of this type which comprise an inductance and a capacitor to produce a ltering effect for a desired frequency or range of disturbing frequencies.

A known construction of a tuned filter utilizes the inherent series inductance of the connecting leads from a capacitor unit to its terminal posts to produce a series resonance effect for a desired frequency or band of frequencies to be eliminated. Since, however, the inherent series inductance varies substantially in different types and sizes of capacitors and may even be different in capacitors of the same type, it is necessary to select a capacitor of suitable design in order to obtain a desired filtering effect or characteristic.

Moreover, since the capacity determines the effectiveness of the filter action and, in particular', the range or band of the frequncies being weakened or suppressed, at best only a comi promise solution may be obtained with this type of tuned filter which affords little iiexibility in adapting it to and complying with the varying requirements and. conditions encountered in practice.

Among the objects of the present invention is,

therefore, to provide a tuned noise or anti-interference filter which is both simple in design as well as compact and rugged in construction; which can be manufactured inexpensively; which is substantially unaffected by uid or moisture penetration or the like; and which may be designed in a simple manner for a desired frequency or range of frequencies to be reduced or eliminated.

beyond a certain cut-off point determined by the values of the inductance I and the capacity C."l

2 The inductance I is directly connected in series with the line or circuit L to be protected and the condenser C serving as a by-pass is connected between said line, preferably at the entrance point of the inductance, and ground G.

Figure 2 shows a construction of filter of the kind shown in Figure 1 in which the straightthrough or main line conductor has the form of a relatively heavy wire It wound into a cylindrical coil or helix and having projecting ends l l and l2 substantially in line with the axis of the helix. This coil has an inductance determined by its dimensions.

Coil I0 is mounted within a cylindrical metal casing I3 having at one end an inturned annular ange I3. One or more layers i4 of insulating material, such as paper or the like, are provided between the coil and the casing in such a manner that the coil fits snugly in the casing and is insulated therefrom. Alternatively, coil l@ may be Wound in a known way on a hollow cylinder of insulating material.

In the construction shown, the coil comprises a Wire of suliicient diameter to result in a substantially rigid and self-supporting structure, supporting the entire filter unit including the enclosing casing and the sealing and terminal structure described hereafter.

An externally threaded metal sleeve l5 nts over the end. l2 of the coil IB so as to extend with the end l2 beyond the end of the casing. An internally threaded metal washer I6 is secured to the inner end of the sleeve l5, i. e., on the end adjacent to the coil it. A resilient washer I'l of cork or the like is interposed between the washer I6 and the inside of flange i3 of the casing, while a further rigid insulating washer ll, for example of Bakelite or the like, is provided on the outside of ange I3. .A further metal washer i8 is placed over the sleeve l5 before a clamping nut 20 by means of which all the washers are clamped up to hermetically seal the casing against sleeve l5 and the coil end l2.

The opposite open end of casing l@ is closed by a metal cap 2l soldered or otherwise connected thereto and having an inturned .annular flange 22 with a resilient insulating washer 2S placed against its inside surface and a rigid insulating washer 24 followed by a metal washer 25 engaging the outside surface of flange 22. The washers 23, 24 and 25 are compressed into firm engagement to provide a tight seal for the casing in any convenient manner. Thus, as shown, a

vtubular rivet 26 is used through which the projecting coil end ll extends and to which may be 

